The present invention relates to an alkoxylation catalyst and a method for producing the same, and a method for producing an alkylene oxide adduct using the catalyst. More particularly, the invention relates to an alkoxylation solid catalyst comprising a metal oxide, and to a method for producing an alkylene oxide adduct that is useful as a chemical material for a surfactant or the like.
A compound in which an alkylene oxide is added to an organic compound having an active hydrogen or to an ester is widely used as a chemical material for surfactants, solvents, or the like. Particularly, those obtained by polyalkoxylating alcohol, fatty acid, fatty acid ester, amine, alkylphenol, or the like with an alkylene oxide such as ethylene oxide or propylene oxide have been utilized as nonionic surfactants in a wide range of application.
As such an alkylene oxide adduct, one having a narrow adduct distribution has many advantages, e.g. high foamability, as compared with one having a wide adduct distribution. As a method for obtaining an alkylene oxide adduct having a narrow adduct distribution, those using a halide catalyst such as a halide of boron, tin, antimony, iron, or aluminum, or an acid catalyst such as phosphoric acid or sulfuric acid are well known. However, in such a method using an acid catalyst, sufficiently narrow adduct distribution cannot be obtained, and a large amount of by-product such as dioxane, dioxolane, or polyethylene glycol is produced. In addition, such an acid catalyst strongly corrodes materials of equipment.
Accordingly, as a solid catalyst for producing an alkylene oxide adduct having a narrow adduct distribution, the following composite oxides have been proposed.
1) Japanese Published Unexamined Patent Application No. (Ibkkai hei) 1-164437: A method for producing an alkylene oxide adduct having a narrow adduct distribution uses as a catalyst a magnesium oxide in which a metal ion such as aluminum is added. It discloses, for example, a magnesium oxide catalyst containing 3 wt. % of aluminum.
2) Japanese Published Unexamined Patent Application No. (Ibkkai hei) 2-71841: A method for producing an alkylene oxide adduct having a narrow adduct distribution with a calcined hydrotalcite as a catalyst is disclosed. The calcined hydrotalcite can be obtained by cacining a natural or synthetic hydrotalcite.
3) Japanese Published Unexamined Patent Application No. (Ibkkai hei) 7-227540: A method for producing an alkylene oxide adduct with a magnesium oxide containing zinc, antimony, tin, or the like as a catalyst, in which generation of a by-product (polyethylene glycol) is inhibited, is disclosed. By using the Mgxe2x80x94Zn, Mgxe2x80x94Sb or Mgxe2x80x94Sn composite oxide catalyst, the amount of polyethylene glycol formed as a by-product can be reduced, although the catalytic activity may be decreased as compared with a case using a magnesium oxide catalyst in which aluminum is added. However, the effect of inhibiting polyethylene glycol formation is still insufficient.
4) Japanese Published Unexamined Patent Application No. (Tokkai hei) 8-268919: A method for producing an alkylene oxide adduct having a narrow adduct distribution uses as a catalyst an Alxe2x80x94Mg composite oxide which is obtained by cacining aluminum magnesium hydroxide.
An alkylene oxide adduct obtained using each of the above-mentioned catalysts has a narrower adduct distribution than that obtained with an acid catalyst. Moreover, generation of a by-product such as dioxane can be inhibited. Particularly, a composite oxide of magnesium and aluminum has a high activity. However, the composite oxide catalyst cannot inhibit formation of polyalkylene glycol as a by-product. Japanese Published Unexamined Patent Application No. Tokkai hei) 7-227540 discloses a catalyst capable of reducing the amount of polyalkylene glycol formed as a by-product. However, the effect of inhibiting polyethylene glycol formation is still insufficient. Moreover, it is a high molecular weight polyalkylene glycol with a molecular weight of several tens of thousands that causes particularly difficult problems. Even a trace of high molecular weight polyalkylene glycol can cause problems in polyalkoxylating. For example, removing catalysts may become difficult, and the stability of a product containing the alkylene oxide adduct may be reduced. Moreover, a catalyst for producing an alkylene oxide adduct is required to have a sufficient catalytic activity in practical use.
Accordingly, it is an object of the present invention to provide a catalyst with which an alkylene oxide adduct having a narrow adduct distribution can be produced more advantageously from an industrial standpoint and a method for producing the same, and a method for producing an alkylene oxide adduct using the catalyst. Particularly, it is an object of the present invention to provide a catalyst with which an alkylene oxide adduct having a narrow adduct distribution can be produced efficiently while inhibiting formation of high molecular weight polyalkylene glycol.
As a result of earnest research with respect to an alkoxylation catalyst suitable for production of an alkylene oxide adduct having a narrow adduct distribution, the inventors have found that it is possible to achieve both high catalytic activity and inhibition of high molecular weight polyalkylene glycol formation with a catalyst prepared by adding a particular metal to a Mgxe2x80x94Al composite oxide.
Thus, a first alkoxylation catalyst of the present invention comprises a metal oxide containing magnesium, aluminum, and at least one metal selected from the metals that belong to group VIA, group VIIA, and group VIII.
The above-mentioned metal added to the Mgxe2x80x94Al composite oxide is selected from those elements that belong to group VIA (chromium, molybdenum, and tungsten), group VIIA (manganese, technetium, and rhenium), and group VIII (iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum) in the periodic table according to a subgroup system.
The alkoxylation catalyst of the present invention is obtained by adding the metal as a third component to Mgxe2x80x94Al composite oxide containing simultaneously a basic site of an oxygen atom adjacent to a magnesium atom for activating an organic compound having an active hydrogen, and an acidic site of an aluminum atom for activating an alkylene oxide. Mgxe2x80x94Al composite oxide has been conventionally utilized, and it is a highly active catalyst with which an alkylene oxide adduct having a narrow adduct distribution can be produced. Moreover, according to the present invention, formation of high molecular weight polyalkylene oxide glycol as a by-product can be inhibited by the third component. This is because the addition of the metal as a third component causes a structural change in the active site of the side reaction. The structure of the active site in the catalyst is changed, for example, by forming a spinel-type structure that includes the third component metal and aluminum.
A second alkoxylation catalyst of the present invention comprises a metal oxide containing magnesium, aluminum, and M (M is at least one selected from the metal elements other than magnesium and aluminum). The metal oxide includes a spinel-type structure that contains aluminum and M.
The metal oxide having the spinel-type structure is represented, for example, by a chemical formula MAl2O4. The metals belonging to groups VIA, VIIA, or VIII can be employed as M, but it is not particularly limited. Two or more types of elements also may be used as M.
The presence of the above-mentioned spinel-type structure can be confirmed by X-ray diffraction analysis. It is preferable that the catalyst includes an oxide in which an X-ray diffraction peak resulting from a rock-salt structure of a magnesium oxide is observed as well as an X-ray diffraction peak resulting from a spinel structure.
Thus, by using at least one of the catalysts of the present invention, it is possible to produce an alkylene oxide adduct having a narrow adduct distribution efficiently, while inhibiting formation of high molecular weight polyalkylene glycol as a by-product. Furthermore, the method for producing an alkylene oxide adduct according to the present invention comprises adding an alkylene oxide to an organic compound in the presence of the alkoxylation catalyst of the present invention.
Furthermore, the method for producing an alkoxylation catalyst comprising a metal oxide according to the present invention comprises: forming a precipitate containing elements of magnesium, aluminum, and at least one element selected from the metal elements belonging to groups VIA, VIIA, and VIII from a mixed aqueous solution containing the elements; and burning the precipitate at a temperature of 300 to 1000xc2x0 C. so as to obtain the metal oxide.